Conversion of heat-sensitive alloys with aid of a thermal barrier



March 3, 1964 c. J. HAVEL 3,122,828

CONVERSION OF HEAT-SENSITIVE ALLOYS WITH AID OF A THERMAL BARRIER Filed Jan. 14, 1965 NVENTOR.

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Mao/4. 5% P PM 4&4 Wa /V 575 United States Patent 3,122,823 CGNVERSION 0F HEAT-dENSI'iiVE ALLQYS WEEH All 9F A DARREER Charles 3. Havel, Utlca, N.Y., assiguor to Special Metals, Inc, New Hartford, N.Y. a corporation of Delaware Filed l'an. 14, 1963, Ser. No. 251,243 6 Claims. (Cl. 29-423) This invention relates to the art of converting ingots of heat-sensitive alloysin particular, heat-sensitive nonferrous and ferrous alloys into plates, sheets, rods, bars or other standard shapes. By

neat-sensitive is here meant alloys having a relatively narrow temperature range of hot-working. Illustrative but non-limiting examples of heat-sensitive alloys the conversion of which is very substantially improved by the carrying out of the present invention are nickel-base alloys of th so-called unworkable class, Udimet 700, Udimet 500, a variety of titanium alloys and certain cobalt-containing steels and certain tool steels of which BR4 is an outstanding example.

in the conventional procedure, the conversion of ingots of such heat-sensitive alloys is relatively slow and laborious. This is because these alloys tend to become embrittled, due to cooling, during the Working steps, and their conversion conventionally requires very frequent conditioning steps between stages of reduction. Again, in following the conventional conversion procedure, conditioning operations to remove surface roll tears--es'pecially, tears at billet cornersnecessarily are numerous, res ng in loss of valuable material (alloy) as well as con tributing to high labor cost. For example, in converting to one inch bar stock an ingot three and three-eighths inches in diameter of a non-ferrous nickel-base alloy, having the following approximate composition:

ALLOY COMPOSlTlON #1 Percent Balance, substantialy all Ni the conventional (i.e., hitherto standard) procedure was as follows:

(1) Cast 22.; ingot 3%" diameter x taper. (2) Roll to 2%" square /s" reduction per heat cats.

(3) Condition all over.

(4) Roll to 2%" square%" reduction per heat5 heats.

(5) Condition all over.

(6) Roll to 1% square /s" reduction per heat-4 heats.

(7) Condition all over rop hot top.

(8) Roll to 1% square /s" reduction per heat2 heats.

(9) Condition all over.

(10) Roll to 1 /8" square-Vs" reduction per heat2 heats.

(11) Condition all over.

(12) Roll to final barcenterless grind.

Summary (a) 19 heatsl8 cogs, 1 final roll (b) 5 laydowns for conditioning (0) Standard yield 48% of poured weight of ingot.

I have discovered that if loss of heat from the heated heat-sensitive alloy ingotand especially the setting up of a relatively steep thermal gradient as between the interior of the ingot and its surface layercan be significantly de- 3,122,323 l mented Wins. 3, 1964 layed it not prevented the workability of the alloy metal is (or, may be) greatly improved. I made this discovery with reference to cladding the ingot with a thick-walled envelope, more particularl with a thick-walled envelope of low-carbon steel. I found that ingots so protected can be converted (cogged, rolled, ground) with a minimum of laydowns for conditioning and with heavier reduction per heat and, at the same time, with a very materially larger yield of product based on the poured Weight of the ingot. As will, of course, be understood by anyone skilled in this art, the composition of the envelope used in this way must be inert at all Working temperatures.

1 have found that the advantageous thermal barrier eiiect of the envelope can be realized, with a great saving in over-all costs, by carrying out the improved procedure about to be described. My improved procedure consists essentially in (a) enveloping the ingot within a relatively very thick-walled sleeve of suitable metal, e.g., steel (i.e., a can having a Wall thickness of the order of 0.75 inch); (5) subjecting the canned ingot to an extrusion or deepdrawing operation which reduces the diameter of the sleeve 'and'brings the latter into the most intimate overall contact with the surfaces of the ingot; (c) hot-rolling the canned ingot nearly to desired dimensions of the enveloped billet of heat-sensitive alloy; (d) stripping off the can; and (e) rolling to final dimensions and centerlessly grinding. In some fact situations, a condi ioning step may be desirable between steps (d) and (e), but I have found thatin generalno conditioning step is necessary at this stage. I have found in actual practice that the number or re-heats may be lessened by as much as percent, and that the over-all yield of finished stock may be increased from the conventional yield of say 48% to as much as 6065%.

The invention will now be described in further detail and with reference to the accompanying drawing, in which The single figure diagrammatically represents an operable mode of carrying out the principles of the present invention.

In the drawing, 1 represents a six inch (1.13.) steel pipe having a wall thickness of approximately 0.75 inch, into which there have been slipped three ingots, 2:2, 2' and 2" of the aforesaid nickel-base alloy, each ingot having a diameter of 5.75 inches and each representing approximately 96 lbs. of alloy. The ingots had been hot top cropped prior to insertion into the pipe, the length of which latter had been chosen so that the pipe would snugly accommodate the three ingots. The ends of the pipe were sealed shut by means of circular steel discs 3, 3' welded at 4, 4, 4, 4, to the ends of the pipe ll.

In carrying out the procedure, the cylindrical ingots 2, 2, 2" are cast in specially prepared molds, are hot top cropped, and then are slid into the thiclowalled steel pipe 51, as many ingots being placed in each pipe as needed for producing an extrusion billet of any desired length.

The ends of pipe 1 are sealed shut by welding on discs 3, 3 of 0.5 inch steel plate.

The resulting article is then extruded or drawn through a round die having such a diameter-preferably, about 3.5 inchesthat the diameters of steel pipe 1 and ingots 2, 2, and 2" are so reduced that the pipe is pressed into the most intimate over-all contact with the contained ingots, thereby producing a master billet 3.5 inches in diameter. Then the extrusion usually is cut to appropriate lengths of clad billet pieces.

:These clad billet pieces are rolled through a cogging mill to 1.25 inches square, in one (1) heat. Thereafter, the steel pipe (can) is removed from the bar-shaped pieces, by high-temperature scaling in a heat-treatment furnace, or by mechanical stripping or by pickling or grinding or by a combination of two or more of these measures, and the bar-shaped pieces may-but frequently need not-he finally conditioned all over and, if necessary, rolled to final dimensions. Finally the pieces may, if desired, =be centerlessly ground and be conditioned all over and finish-rolled.

My improved procedure may be compared. with the hereinabove standard procedure as follows:

Improved Procedure Cast diameter x 96# ingot. Crop hot top. Can in 5% 1D. x 7%" OD. pipe (3 ingots per can).

-(4) Extrude or draw to 3 /2" diameter. (5) R011 to 1 A square-1 heat. (6) Strip can. (7) Heat and roll to final bar.

Summary tion of the effectiveness of this invention, it is necessary that the thermal barrier wall have a thickness of at least /6 of an inch after the last rolling operation. Preferably the thick-walled thermal barrier has a wall thickness of at least of an inch at the start, and a wall thickness of at least A of an inch after the extrusion or drawing operation, and a wall thickness of of an inch after repeated rollings. This is in contrast to conventional canning in which the wall thickness may be as much as 0.06 inch at the start, and be reduced to 0.01 inch after extrusion, and ending up with a wall thickness of about 0.001 inch at the conclusion of the rolling operations.

Due to the eificiency of this thermal barrier, reductions trom 3.5 inches diameter to as much as 1.25 inch have, to date, been routinely eifected, without re-heating and without surface tearing, and greater reductions appear probable. This is in contrast to a maximum of 0.125 inch reduction, per heat, in the case of un-clad ingots of the same alloy composition. In addition, ingots of the heat-sensitive alloys have been converted to round (or, r

is that the same must be materially more malleable than is the enshrouded alloy composition being rolled. Aside from this critenion, and from the obvious criterion that the enshrouding material must be inert with respect to the composition of the clad billet, there appears to be no limit to the composition of the enshrouding metal.

In the above disclosure, it has been emphasized that the conversion of the ingot or billet while enshrouded in relatively very thick-walled envelope prevents the generation of cracksespecially, the generation of tears at billet corners-during the working of the billet to final form. Another, and very surprising result of the carrying out of the process of the present invention is the lessening of the load necessary for converting the ingot or billet to final form. Thus I have found that rolling with the thermal protector of the present invention reduces the mill (power) load by as much as 40% enabling conversions to be carnied out on equipment which normflly would be inadequate. I believe that the diminution in power requirement stems from the circumstance that the cogging rolls readily bite into the relatively very malleable envelope material-thereby clearly promoting the rolling operation-as opposed to the unclad surface of the ingot or billet being converted. I

It is to be appreciated, then, that the practice of the present invention serves ver substantially to lower the over-all cost of converting heat-sensitive alloy ingots and billets.

The extrusion step may be carried out using conventional apparatus and following conventional extrusion procedure. The cogging mill used for rolling the clad billet pieces may be equipped with either diamond, square or gothic passes.

It is to be appreciated that the improved process of the present invention is not restricted to converting in- 'gots ofany specific size or form, or of the specific alloy composition chosen for illustrative purposes in the above specific example. Rather, the procedure is equally applicable to heat-sensitive alloys generally, includingas further illustrations of the scope of operability of the processthe following particular compositions:

ALLOY #2 Percent C 0.38 Mn 1.50 Si .70 Cr 20.0 Ni 20.0

Mo 4.0 \V 4.0 Cb 4.0 Fe 3.0 Balance substantially all cobalt.

ALLOY #3 Percent M0 4.0 Balance substantially all Ti.

ALLOY #4 Percent Al 6.0 V 4.0 Balance substantially all Ti.

ALLOY #5 Percent M0 1.2 Ni max 5 Balance substantially all Fe.

Finally, it is to be explained that the hereinabove described thermal barrier effect is not realized by conventional cladding of the sort adapted to prevent unwanted oxidation of the metal undergoing conversion, in

which conventional procedures an ingot is clad with a with the conversion of an ingot conventionally clad in a 16-20 gauge can, I found that the necessary heats were reduced from, say 19 (for un-clad ingot) only to 18 or 17 (for the thin-walled cladding), whereas an ingot of identical alloy composition but canned in a protected skin of thick-walled (0.75 inch wall thickness) pipe made it possible to convert the ingot to the same final product in a total of only 3 heats.

I claim:

1. In the process of converting an ingot of heat-sensitive alloy composition involving rolling the ingot while at a temperature above the critical temperature of the alloy, the improvement which consists in enveloping the ingot in a metal shell having such wall thickness as materially to retard the setting up of a sharp temperature difierential between surface and interior of the ingot, hot-extruding or drawing the so-enveloped ingot through an extrusion or drawing die having such a size of opening as to compress said shell onto said ingot and materially to reduce the cross-sectional area of the enveloped ingot; thereafter hot-rolling the extruded or drawn article to approximately final cross-sectional size without in-process conditioning; and removing the shell from the resulting reduced billet.

2. In the process of converting an ingot of heat-sensitive alloy composition involving rolling the ingot while at a temperature above the critical temperature of the alloy, the improvement which consists in enveloping the ingot in a metal. shell having such wall thickness as materially to retard the setting up of a sharp temperature difierential between surface and interior of the ingot, extruding or drawing the so-enveloped ingot through an extrusion or drawing die having such a size of opening as to compress said shell onto said ingot and materially to reduce the cross-sectional area of the enveloped ingot; thereafter rolling the extruded or drawn article to approximately final cross-sectional size without in-process conditioning; removing the shell from the resulting reduced billet and finish-rolling the un-clad article.

In the process of converting an ingot of heat-sensitive alloy composition involving rolling the ingot while at a temperature above the critical temperature of the alloy, the improvement which consists in enveloping the ingot in a metal shell having such wall thickness as materially to retard the setting up of a sharp temperature differential between surface and interior of the ingot, extruding or drawing the so-enveloped ingot through an extrusion or drawing die having such a size of opening as to compress said shell onto said ingot and materially to reduce the cross-sectional area of the enveloped ingot; thereafter rolling the extruded or drawn article to approximately final cross-sectional size without in-process conditioning; and removing the shell from the resulting reduced billet conditioning all over and finish-rolling the un-clad article.

4. The improved process defined in claim 1, in which the shell is composed of a metal having substantially greater malleability than that of the alloy composition of the ingot.

5. The improved process defined in claim 1, in which the wall thickness of the shell is at least 0.0625 inch at the conclusion of the rolling operations.

6. The improved process defined in claim 1, in which the wall thickness of the shell, as applied to the ingot, is of the order of 0.75 inch, and in which the wall thiCs ness of the shell is reduced to about 0.25 inch by the extrusion or drawing operation.

References Cited in the file of this patent UNITED STATES PATENTS 470,623 Levez Mar. 8, 1892 2,064,684 Ostendorf Dec. 15, 1936 2,423,810 Goulding July 8, 1947 

1. IN THE PROCESS OF CONVERTING AN INGOT OF HEAT-SENSITIVE ALLOY COMPOSITION INVOLVING ROLLING THE INGOT WHILE AT A TEMPERATURE ABOVE THE CRITICAL TEMPERATURE OF THE ALLOY, THE IMPROVEMENT WHICH CONSISTS IN ENVELOPING THE INGOT IN A METAL SHELL HAVING SUCH WALL THICKNESS AS MATERIALLY TO RETARD THE SETTING UP OF A SHARP TEMPERATURE DIFFERENTIAL BETWEEN SURFACE AND INTERIOR OF THE INGOT, HOT-EXTENDING OR DRAWING THE SO-ENVELOPED INGOT THROUGH AN EXTRUSION OF DRAWING DIE HAVING SUCH A SIZE OF OPENING AS TO COMPRESS SAID SHELL ONTO SAID INGOT AND MATERIALLY TO REDUCE THE CROSS-SECTIONAL AREA OF THE ENVELOPED INGOT; THEREAFTER HOT-ROLLING THE EXTRUDED OR DRAWN ARTICLE TO APPROXIMATELY FINAL CROSS-SECTIONAL SIZE WITHOUT IN-PROCESS CONDITIONING; AND REMOVING THE SHELL FROM THE RESULTING REDUCED BILLET. 